This invention relates to steam vaporizers and more particularly to improvements in steam vaporizers of the type in which an electric current is passed through a liquid such as water to heat the liquid to its boiling point for generating steam.
Steam vaporizers are commonly used in sick rooms to relieve colds, bronchitis, and other respiratory ailments. Often, such vaporizers are used in the home, for example, in the bedrooms of small children. Steam vaporizers are also sometimes used as a room humidifier. A common type of electric steam vaporizer includes a pair of parallel electrodes which are mounted to extend into a water reservoir. An electric current is passed between the electrodes to heat the water for generating steam. The electrodes are commonly surrounded with a cylindrical tube for defining a boiling chamber having an appriciably smaller volume than the reservoir. However, there has been difficulty in confining the heat to the boiling chamber in prior art vaporizer designs. There is considerable hazard to a patient using the vaporizer when water in the reservoir or receptical at a location exterior to the boiling chamber becomes very hot after prolonged use. One solution to this problem has been to provide an annular air or water-filled insulating chamber between the boiling chamber and the liquid reservoir. The boiling chamber is then completely enclosed, except for a small opening into the reservoir to permit replenishment water to flow into the boiling chamber. However, there is still considerable heat transferred from the boiling chamber to the reservoir due to a liquid surging action through the replenishment water opening. Water surges back and forth between the boiling chamber and the reservoir while the vaporizer is operated. This surging action causes heated water from the boiling chamber to enter the reservoir, thereby increasing the temperature of the water in the reservoir. Also, cooler reservoir water enters the boiling chamber to lower the efficiency of the boiling chamber.
Another problem with prior art steam vaporizers of this type is the erratic occurrence of "spitting" or, in other words, the emission of hot water droplets along with the steam. This is undesirable since the water droplets are commonly hot enough to cause burns and the steam vaporizers are often used to relieve respiratory problems in children and invalids. It has been found that spitting can be caused by a build-up of foam on the water surface above the boiling chamber caused by minerals and other impurities within the water. In the past, spitting sometimes has been prevented by adding anti-foaming agents to the water in the vaporizer. By destroying surface tension, foam generation is prevented which, in turn, eliminates spitting. However, the use of anti-foaming agents results in additional expense and additional maintenance steps must be taken by the operator of a steam vaporizer.
In the past, steam vaporizers have generally been constructed from a relatively hard synthetic resinous material, such as a phenolic resin. However, materials of this type are relatively expensive compared to some softer thermoplastic materials. It is desirable to manufacture steam vaporizers from softer synthetic resinous materials such as polypropylene to reduce the cost of the vaporizers. However, materials such as polypropylene flow easily under pressure. As a consequence, it is difficult to mount the electrodes in a vaporizer formed from polypropylene so that the electrodes are maintained in a fixed, parallel relationship while heated to the boiling point of water. Prior art techniques for mounting electrodes in a vaporizer with screws or bolts are not acceptable in a vaporizer formed from polypropylene, for example, due to its flow characteristics which may permit the electrodes to move from their parallel relationship and may permit compression type electrical connections to loosen.